Many modern diesel engines have an exhaust system that features an exhaust gas recirculation (“EGR”) system that routes a portion of engine exhaust gas into an air intake system, such that a mixture of fresh air and engine exhaust is supplied to a combustion chamber during engine operation. EGR helps to reduce certain emissions from the engine, such as Nitrous Oxides (NOx). In addition to EGR rate, certain other engine operating parameters are also controlled in order to reduce engine emissions. These parameters include fuel injection timing, and intake air flow rates.
It has been found that controlling engine operating parameters to reduce NOx emissions has an adverse effect of increasing particulate matter emissions, Similarly, controlling engine operating parameters to reduce particulate matter emissions has an adverse effect of increasing NOx emissions. As both NOx emissions and particulate matter emissions are regulated, control of engine operating parameters must be balanced so that the engine does not produce excessive amounts of either NOx emissions or particulate matter emissions. It has been found that control of NOx emissions is more important during transient engine operations, i.e, while an engine is undergoing many engine speed changes and torque output changes, such as during acceleration, while control of particulate matter is more important during steady state operating conditions, i.e., while an engine is operating at a generally constant speed and torque output, such as during highway driving. Therefore, a need exists for a method and system to determine if an engine is operating in transient operating conditions and adjust engine operating parameters when transient operating conditions are occurring.